KEY POINTS
- This planning study compared paired supine and upright computed tomography scans from 12 healthy male volunteers, aged 32–68 years.
- Carbon ion plans used two opposed lateral fields and prescribed relative biological effectiveness-weighted doses of 51.6 Gy to the primary planning target volume and 43.9 Gy to the surrounding target subvolume in 12 fractions.
- Mean absolute differences between upright and supine plans for clinical target volume D2%, D5%, D50%, D95% and D98% were all below 0.15 Gy, corresponding to less than 0.29% of the 51.6 Gy prescription.
- No significant differences were observed in the evaluated target or organ-at-risk dose metrics, dose-volume histograms or contoured volumes between postures (all p > 0.05).
- Robustness against simulated range uncertainty of ±3% and setup uncertainties of ±3 mm or ±5 mm was comparable between upright and supine plans.
CLINICAL TAKEAWAY
Upright positioning could allow prostate carbon ion radiotherapy using fixed beam lines and a rotating chair, potentially reducing reliance on large rotating gantries. However, this was an in silico study in 12 healthy volunteers, and actual upright setup uncertainty, intrafraction motion, reproducibility and clinical outcomes remain untested.